The present invention concerns a process for manufacturing a dimensionally stable, three-dimensionally shaped, sheetlike textile material, the shaped structures obtained by the process, and to the use of the structures as core material in the manufacture of sheetlike sandwich structures.
Sheetlike sandwich structures comprising a core and two cover layers whose core comprises dimensionally stable, three-dimensionally shaped textile materials are already known, for example from FR-A-23 25 503 and EP-A-158 234. The sandwich material described in these references has a core comprising a three-dimensionally shaped, sheetlike textile material with a regular arrangement of a multiplicity of elevations of equal height and a flat top on a base surface. Appreciable differences exist between the core materials known from FR-A-23 25 503 and EP-A-158 234 concerning their structure. While the materials known from FR-A-23 25 503 have an essentially completely closed structure, where not only the textile base areas but also the walls of the elevations distributed over the base area form a solid, pore-free, fiber-permeated resin material, the core materials known from EP-A 158 234 form a network structure of resin-impregnated threads with open loops.
The closed-structure core material known from FR-A-2 325 503 is manufactured by pressing a resin-impregnated laid staple fiber fabric into the desired geometric shape in a compression mold. In this process, a relatively large amount of resin is used, based on the fiber weight, so that the result of the pressing operation is an essentially fiber-reinforced resin structure.
The core material thus obtained has a relatively high weight. It does not permit any gas exchange, and it shows little flexibility.
The network-structured (hereinafter also filigree-structured) core material known from EP-A-158 234 is produced by deep drawing a resin-impregnated, deep-drawable textile material such as a resin-impregnated knitted fabric. This core material known from EP-A-158 234 combines good mechanical stability with low density. It permits free gas exchange between the sides of the sheet and it possesses high flexibility.
As mentioned earlier, the core material known from EP-A-158 234 is manufactured by impregnating a sheetlike textile material with a thermosetting resin, drying the impregnated material to form a prepreg and then forming the prepreg into the desired shape for the core material by a deep-drawing process.
A serious disadvantage of this manufacturing process is that it is difficult to impregnate a deep-drawable sheetlike textile material uniformly with a resin without prestretching the material completely or partially. Such a possibly nonuniform distortion of the textile sheet material results in a lack of deep-drawability and, in the finished product, in partial or complete loss of fiber strength. Similarly, the handling of the still not precondensed, resin-impregnated, deep-drawable textile material can easily result in a partial prestretching of this material with the abovementioned disadvantages for the uniformity of the quality of the end product, unless special precautions are taken. A further disadvantage of this known core material is that it is not readily recyclable. The manufacturing and recycling problems to some extent prevent wider use of these otherwise perfectly favorable core materials. The present invention overcomes the disadvantage of this known core material and the manufacture thereof.